The present invention relates to the manufacture of tooling (such as molds or dies) and in particular to the manufacture of tooling for use in casting, stamping and/or molding high volume production articles (such as plastics components).
EP-A-0781625 discloses a technique for manufacturing tooling in which a ceramic model is formed to have a shape in the form of a component to be produced by the tooling. The ceramic model is used as the substrate upon which tool steel is sprayed to produce a tool steel mold for production purposes. The technique described may be used to form, separately, cooperating mold/die tooling parts which mate at an interface to define a mold cavity for production casting, plastics molding or other purposes. One disadvantage with the technique is that some degree of surface finishing (such as by grinding or lapping) of the mating surfaces of the mold/die parts is typically required in order to ensure accurate alignment of the mold/die parts.
An improved technique has now been devised.
According to a first aspect, the invention provides a process for the production of tooling (such as a mold or die) for manufacturing an article, the process comprising:
i) laying a facsimile of the article in register with a first tooling part,; and,
ii) depositing sprayed metallic material over the first tooling part and the facsimile of the article in order to form a second tooling part.
Desirably the first tooling part comprises a metallic material (desirably having a metallic working surface), preferably formed by controlled deposition of sprayed molten metallic material.
The facsimile of the article in register with the first tooling part becomes embedded between the first and second tooling parts, portions of the first and second tooling parts bounding the article facsimile being in metal to metal contact with one another.
The process preferably further comprises separating the first and second tooling parts and also preferably removing the article facsimile from the first tooling part.
Desirably the article facsimile is adhered to the first tooling part prior to step ii).
The article facsimile may be introduced to the first tooling part in fluid form and subsequently cure/harden.
Desirably the article facsimile is cast onto the first tooling part according to step i). Preferably the article facsimile is cast into the first tooling part by vacuum casting. Desirably, the first tooling part is mated with a preliminary forming element enabling the article facsimile to be cast, the preliminary forming element is preferably subsequently removed to leave the article facsimile in register with the first tooling part. The preliminary forming element may for example comprise a negative of one hall of the article facsimile, and may be of a flexible material (facilitating subsequent removal following casting of the article facsimile). For example the preliminary forming element may comprise a silicone rubber mold part as known in the art and used in a variety of rapid prototyping techniques such as the so called xe2x80x98vacuum castingxe2x80x99 technique.
Desirably the article facsimile comprises a refractory material, preferably a ceramic material or freeze castable material. Advantageously, the refractory material is provided as a slurry which subsequently hardens when cast. Desirably, the process preferably includes a hardening procedure which for freeze casting may comprise a freezing stage (and also preferably a drying stage). Suitable materials for the article facsimile have been found to be materials such as dental stone and freeze castable ceramics such as alumina provided in a silica sol, which has been found to be particularly effective. Other suitable materials may, for example, be metal filled epoxy resins.
Ultimately, the first and second tooling parts cooperate to form a mold, tool or die for producing an article, such as for example a plastics component or the like. The first tooling part includes a negative impression of a first portion of the article; following step ii) of the process according to the invention, the second tooling part includes a negative impression of a second portion of the article.
The first tooling part is preferably obtained by depositing molten sprayed metallic material onto a substrate formed of refractory material which material may be the same as the material used to produce the article facsimile previously described.
Desirably, as a precursor, a preliminary mold (which may typically be of non-metallic, preferably flexible material, such as silicone rubber) is obtained having first and second mold parts corresponding to the first and second tooling parts of the metallic tooling. The preliminary mold may for example be a silicone rubber mold of a type use widely in the prototyping field for producing sample components by, for example, vacuum casting of plastics.
The second preliminary mold part is preferably the preliminary forming element with which the first metallic tooling part is mated when casting the article facsimile.
The first preliminary mold part is preferably used to make the first metallic tooling part advantageously by forming a substrate on the first preliminary mold part, the substrate desirably comprising a refractory material (preferably a freeze cast material). The substrate is then removed from the first preliminary mold part. The substrate so formed is then used to form the first metallic tooling part preferably by deposition of molten sprayed metallic material (as described above).
Following spray forming of the first metallic tooling part, the refractory substrate is removed by grit blasting or other suitable means. This provides a surface finish on the working surface of the first tooling part of sufficiently high quality to accept the sprayed metallic material from step ii) but provides a sufficiently clean boundary to enable the first and second tooling parts to be separated following( step ii). Aditionally or alternatively, mechanical separation techniques and/or certain release agents (such as suitable coatings) may be utilized.
The spraying of metallic material to form the first and second metallic tooling parts is preferably carried out using conventional metallurgical spraying apparatus, preferably where the spraying conditions and material are tailored to control stresses set up in the spray deposited metallic material. For example, WO-A-96/09421 discloses a technique of producing metallic articles by sprayforming wherein the conditions are tailored to ensure stress control.
It is preferred that in the sprayforming process action is taken to seal or infill interconnected porosity within the spray deposited first and second metallic tooling parts (particularly ensuring that porosity is sealed at the respective working surface of each mold part). WO-A-97/33012 discloses porosity reduction techniques which may be employed in accordance with the process described herein.
Furthermore, cooling channels may advantageously be incorporated in the first and/or second metallic spray deposited tooling part in order to permit cooling of the mold, thereby reducing the operating cycle time. WO-A-95/19859 discloses a technique for incorporating cooling channels into sprayed metallic deposited material.